ios - 如何使符合已定义协议(protocol)的 UITableViewCells 出队

Question

我想确保我的表格 View 只包含符合所述协议(protocol)的单元格。我简化了实现以说明具体问题。

    protocol ACommonLookAndFeel {
       func configureMyLookAndFeel() 
    }

    CellA: UITableViewCell, ACommonLookAndFeel
    CellB: UITableViewCell, ACommonLookAndFeel

    func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {

        var cell: UITableViewCell   

        if indexPath.row == 0 {          
             cell = tableView.dequeueReusableCellWithIdentifier("CellA", forIndexPath: indexPath) as! CellA
             if let myCell = cell as? CellA {
                 myCell.configureMyLookAndFeel() // we need to call this for each cell
             }
        } else if indexPath.row == 1 {
            cell = tableView.dequeueReusableCellWithIdentifier("CellB", forIndexPath: indexPath) as! CellB
            if let myCell = cell as? CellB {
               myCell.configureMyLookAndFeel() // we need to call this for each cell
            }
        }
        return cell
     }

上面的代码是有效的，除了有重复的代码，我每次都需要进行转换才能访问 configureMyLookAndFeel() 方法。因为我希望我的所有单元格都针对外观进行配置，所以我尝试了下面的代码，但遇到了编译错误

错误:无法将类型“协议(protocol)”的返回表达式转换为返回类型“UITableViewCell”

func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {

    var cell: protocol <ACommonLookAndFeel>   

    if indexPath.row == 0 {          
         cell = tableView.dequeueReusableCellWithIdentifier("CellA", forIndexPath: indexPath) as! CellA
    } else if indexPath.row == 1 {
        cell = tableView.dequeueReusableCellWithIdentifier("CellB", forIndexPath: indexPath) as! CellB
    }

    cell.configureMyLookAndFeel() // works
    return cell // Compiler Error !
 }

1. 有没有办法修复这个编译器错误？

2. 理想情况下，我不想避免重复调用 dequeueCell 和转换为 CellA 或 CellB。我知道我需要根据与我的单元格类名称相同的 cellReuseIdentifier 将其转换到哪个单元格。有办法吗？

谢谢!

Answer 1

试试这个:

func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {

    var cell: UITableViewCell

    if indexPath.row == 0 {
        cell = tableView.dequeueReusableCellWithIdentifier("CellA", forIndexPath: indexPath) // There is no need to cast here
    } else if indexPath.row == 1 {
        cell = tableView.dequeueReusableCellWithIdentifier("CellB", forIndexPath: indexPath) // There is no need to cast here
    }

    // The method will be called for all cells that conform to ACommonLookAndFeel.
    // This is also safe, so no crash will occur if you dequeue a cell that 
    // doesn't conform to ACommonLookAndFeel. Depending on the behavior
    // you want to achieve, you may want to use a ! instead of ? to force
    // a crash in case of issues while developing your app.
    (cell as? ACommonLookAndFeel)?.configureMyLookAndFeel()

    // You have to return a UITableViewCell, not a ACommonLookAndFeel
    return cell 
}